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VFR Alps Crossing

Sparky Imeson’s Mountain Flying Bible remains one of my references – just good common sense on weather, density altitude and do’s and dont’s. Not really a back country guide and aimed at the USA, but the knowledge applies to Europe.

In a fixed gear, fixed prop Cessna suggest you fly early, fly light and understand density altitude. Agree with Peter that upper winds of 10 knots – not that usual, would be ideal. If the free stream wind is above 25 knots suggest caution. Would also advise a 2,000 agl over the passes.

Oxford (EGTK), United Kingdom

There is a rule going around, which I can’t remember, but it is something like needing to have a 1000ft terrain clearance for every 10kt of wind blowing at (this being the worst case) right angle to the ridge, for the vertical speed to be below 500fpm.

OK; a C152 will not be able to hold altitude in a 500fpm downdraught at FL100 (a TB20 would be marginal) but you can choose other routes where you have a greater clearance.

Administrator
Shoreham EGKA, United Kingdom

There is a rule going around, which I can’t remember, but it is something like needing to have a 1000ft terrain clearance for every 10kt of wind blowing at (this being the worst case) right angle to the ridge, for the vertical speed to be below 500fpm.

Peter, I think the first time I read about this was on one of your pages on your website.

Another question: I came across a video today of two pilots doing mountain flying this week. They mention it is good practice to fly close to the mountains. What’s the reason for that? I would have had the tendency to stay away from terrain as much as possible.

Btw. the link to the video, worthwhile watching:



Hungriger Wolf (EDHF), Germany

They mention it is good practice to fly close to the mountains. What’s the reason for that?

So you have the full width of the valley to turn. Should you encounter a downdraft or any other problem, you can turn. Also cross ridges in a 45 degree angle. Just keep in mind: close to a downdraft is an updraft and close to an updraft is a downdraft.

Peter, I think the first time I read about this was on one of your pages on your website.

Also read where he says that he has actually never done any mountain flying (i.e. in the canyons)…

I think the first time I read about this was on one of your pages on your website.

Yeah – I looked for it there but couldn’t find it

But there has to be such a rule, because the max VS of the airflow has to be related to the wind speed and the height above the ridge. It probably won’t be a linear relationship though. And it will depend on how “sharp” the ridge is.

Administrator
Shoreham EGKA, United Kingdom

In a valley, horizontally speaking, one should always stay close to the terrain so as to give you the maximum amount of space should a 180 be required. It’s also recommended for traffic avoidance; in general, one should fly on the righthand side.

As far as vertical clearance is concerned, I would guess that there are mountain pilots, who have never been much above 1000 feet above the ground.
Obviously, much of the “fascination” of mountain flying has to do with being close to the mountains. But that should only be done in benign weather conditions with light winds. And it should ideally be first practiced with an experienced mountain pilot. The sensations can be quite special.

Last Edited by boscomantico at 20 Jul 17:49
Mainz (EDFZ) & Egelsbach (EDFE), Germany

What’s the reason for that?

As always, there are conflicting goals. On one hand, you want to stay close to the terrain so you have the maximum space for a turn back. In the valleys, you often don’t see very far due to geometric reasons, eg. because the valley bends. Last year, an F/A-18 crashed into a mountain, essentially because he underestimated his turning radius. The weather suddenly worsened, his companion saved his backside by climbing almost vertically out into IMC (an option you don’t have with your C152), the other one tried a 180 and failed to fit it into the valley.

On the other hand, there are cables, such as power lines, funiculars and worst, hay cables. Hay cables are used by the farmers to send bundles of hay downhill, and unlike power lines, they are only attached on both ends, but have no supporting masts which could be used to infer the presence of cables. They are pretty much impossible to see. For this reason, you don’t want to be too close to the mountains.

So use common sense. If you don’t see far (a valley bend coming up) and the weather isn’t blue sky, stay close to the mountains, if the weather is good and you see far ahead, stay a bit farther away from the mountains to minimize the risk of hitting a cable.

But for your LNZ-GRZ route, if you fly it at ~8000’, you’re above all peaks, so it isn’t strictly speaking mountain flying.

LSZK, Switzerland

Just keep in mind: close to a downdraft is an updraft and close to an updraft is a downdraft.

That’s why I stopped trying to maintain exact altitudes – I just ride it out, you’ll stay at an altitude on average without having to constantly retrim and repower the airplane. Just set yourself a minimum safe altitude and turn back if you’re unable to maintain above it.

Your C152 unlikely has an autopilot, but if it has one, don’t use it in the mountains, fly by hand to get a feel for the winds, so you won’t be surprised.

LSZK, Switzerland

I had been and crosssed Alps in the eastern section 15+ times – and being flat country origin. My advice is pretty simple – always planGAFOR routes and stay on them. You do not need FL 115 to do that. There are places you can easily take shortcut when you see the weather and terrain below you, but do not make that decision on the planning-unlesss you are bold and have engine which never fail.

LKKU, LKTB

It’s also recommended for traffic avoidance; in general, one should fly on the righthand side.

I’d avoid the downdraft side – downwind of ridge, but in light winds that could be the shade side. A descending turn uses far less valley width. Practice by flying along a road/river/canal, in open country, first at a good altitude, and doing a power-off, airspeed increasing, steep descending turn, starting at glide speed.

Maoraigh
EGPE, United Kingdom
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